The acetals with chemical structure R2—CH—(O—R1)2 are oxygenated compounds produced by the reaction between an aldehyde (R2—CHO) and an alcohol (R1—OH) in the presence of an acid catalyst, accordingly to:

Traditionally, the reaction is catalyzed by mineral or carboxylic acids (U.S. Pat. No. 2,519,540, U.S. Pat. No. 5,362,918 and U.S. Pat. No. 5,527,969). The disadvantage of using soluble catalyst is that they must be neutralized after reaction and separated from the product. Therefore, heterogeneous catalysts as ion exchange resins (acid type) or zeolites are used, which have the advantage of being easily separated from reaction product and having a long lifetime (patents EP 1 167 333 A2 and U.S. Pat. No. 4,579,979).
The synthesis of acetals is a reversible reaction. In order to obtain acceptable acetal yields, the equilibrium must be displaced in the direction of acetal synthesis. Several methods are used to displace equilibrium towards acetal formation, such as:    1. to use a large excess of one of the reactants, in general the alcohol, which then requires elimination of that excess in a step of purification of the desired product (U.S. Pat. No. 5,362,918);    2. to use an organic solvent to eliminate water by azeotropic distillation between a solvent and water or by liquid-liquid extraction, a further step of separation is necessary to remove the solvent from the end product (U.S. Pat. No. 2,519,540, U.S. Pat. No. 4,579,979, U.S. Pat. No. 5,362,918 e U.S. Pat. No. 5,527,969);    3. to use reactive separations in order to remove the products from the reaction medium, being the reactive distillation process the most common (U.S. Pat. No. 5,362,918).
The processes described above introduce some improvement in the acetals production; however, they also have several disadvantages. For the first method, the conversion of the limiting reactant increases but the yield of the reaction decreases. The second one presents higher conversions but it is necessary to use a solvent; consequently, the costs of raw materials and equipment increase. The reactive distillation could not be applied to all systems, due to azeotropes formation and/or to the incompatible volatilities of reactants and products. It is also possible by-products formation.
In recent times, in addition to the well-known acetals applications, they have been considered as diesel oil additives, mainly acetaldehyde diethylacetal. It is confirmed that the use of acetals decreases the emissions of particles and NOx while keeping or improving the cetane number and helping in the combustion of the final products, without decreasing the ignition quality (patents DE 2 911 411, DE 3 136 030, WO 2001/181 154 A1, WO 2002/026 744 A1).